Propulsion Control Device

Abstract

This propulsion control device (80) comprises: a filter capacitor (6) that smoothes an overhead line voltage applied from an overhead line (1); an inverter (7) which is connected in parallel with the filter capacitor (6) and which applies a variable-voltage and variable-frequency AC voltage to a propulsion motor (8) mounted on a railway vehicle, and a control unit (12) that controls the inverter (7) on the basis of the overhead line voltage and the filter capacitor voltage. When the overhead line voltage exceeds a first threshold value during a regeneration operation of the propulsion motor (8), the control unit (12) carries out regenerative power control to lower, to below a command voltage, the motor applied voltage to be applied to the propulsion motor (8).

Description

[Technical Field]

[0001] The present disclosure relates to a propulsion control device mounted on a railway vehicle. [Background technology]

[0002] In recent years, improvements in energy-saving performance have been pursued in a variety of systems. The same is true for propulsion control devices, where efforts are being made to improve the efficiency of propulsion control devices by using SiC (Silicon Carbide) devices in the power conversion equipment installed in the propulsion control devices and by using permanent magnet synchronous motors in the propulsion motors installed in the propulsion control devices. One way of pursuing improvements in system efficiency is regenerative power control, which attempts to return as much regenerative power generated by the propulsion motor as possible to the overhead lines when the railway vehicle decelerates.

[0003] On the other hand, even if regenerative power is to be returned to the overhead lines, if there are no other railway vehicles nearby that can consume the regenerative power, a situation may arise in which the regenerative power cannot be returned to the overhead lines in order to suppress an increase in overhead line voltage. If this situation continues, regenerative braking will be disabled, and the railway vehicle will need to obtain braking force solely through friction brakes. However, excessive use of friction brakes has the disadvantage of increasing brake shoe wear and shortening the maintenance intervals for the railway vehicle. Therefore, in conventional railway vehicles, as shown in Patent Document 1 below, for example, a brake resistor provided in a brake chopper circuit is used to consume excess power generated by regenerative braking that cannot be used by other trains. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-126039 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, current regenerative power control in propulsion control devices is highly dependent on brake chopper circuits. Therefore, consuming the increased regenerative energy resulting from the recent trend toward energy conservation leads to an increase in the size of the brake chopper circuits. Furthermore, avoiding an increase in the size of the brake chopper circuits increases reliance on friction brakes, which increases brake shoe wear and shortens the maintenance intervals for railway vehicles. Therefore, there is a need for a regenerative power control technology that can prevent the increase in the size of brake chopper circuits and the shortening of maintenance intervals for railway vehicles in propulsion control devices.

[0006] The present disclosure has been made in view of the above, and aims to provide a propulsion control device that can suppress an increase in the size of a brake chopper circuit and a shortening of maintenance intervals for railway vehicles. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the object, a propulsion control device according to the present disclosure includes a filter capacitor, an inverter connected in parallel to the filter capacitor, and a control unit. The filter capacitor smoothes the overhead line voltage applied from the overhead line. The inverter applies a variable voltage and variable frequency AC voltage to a traction motor mounted on a railway vehicle. The control unit controls the inverter based on the overhead line voltage and the filter capacitor voltage, which is the voltage of the filter capacitor. Furthermore, when the overhead line voltage exceeds a first threshold during regenerative operation of the traction motor, the control unit implements a first control that reduces the motor applied voltage applied to the traction motor below a command voltage. [Effects of the Invention]

[0008] The propulsion control device according to the present disclosure has the effect of suppressing an increase in the size of the brake chopper circuit and a shortening of the maintenance interval of the railway vehicle. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a railway vehicle drive system including a propulsion control device according to a first embodiment; [Figure 2] FIG. 2 is a diagram showing an example of the configuration of a PWM signal generating unit provided in the control unit shown in FIG. 1; [Figure 3] FIG. 3 is a diagram illustrating the operation of pulse mode switching processing in the PWM signal generating unit shown in FIG. 2. [Figure 4] FIG. 10 is a diagram showing an operating curve for explaining regenerative power control according to the first embodiment. [Figure 5] 1 is a time chart illustrating regenerative power control according to the first embodiment; [Figure 6] 1 is a flowchart illustrating regenerative power control according to the first embodiment. [Figure 7] FIG. 1 is a block diagram showing an example of a hardware configuration for realizing the functions of a control unit according to a first embodiment. [Figure 8] FIG. 10 is a block diagram showing another example of a hardware configuration for realizing the functions of the control unit according to the first embodiment. [Figure 9] FIG. 10 is a diagram showing an operating curve for explaining regenerative power control according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a propulsion control device according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[0011] Embodiment 1 FIG. 1 is a diagram showing an example configuration of a railway vehicle traction system 100 including a propulsion control device 80 according to a first embodiment. In FIG. 1, the railway vehicle traction system 100 is composed of an overhead line 1, a current collector 2, a propulsion control device 80, and a traction motor 8. The propulsion control device 80 includes switches 3a and 3b, a filter reactor 4, a brake chopper circuit 5, a filter capacitor 6, an inverter 7, voltage detectors 9 and 10, a current detector 11, and a control unit 12. The current collector 2, the propulsion control device 80, and the propulsion motor 8 are mounted on a railway vehicle (not shown). The propulsion motor 8 is provided with a speed detector 16.

[0012] The overhead line 1 applies a DC voltage between a high-potential DC bus 14a and a low-potential DC bus 14b. Switches 3a and 3b and a filter reactor 4 are inserted into the high-potential DC bus 14a. An example of the switch 3a is a circuit breaker, and an example of the switch 3b is a line interrupter. A filter capacitor 6 is connected between the high-potential DC bus 14a and the low-potential DC bus 14b. The overhead line voltage, which is a DC voltage output by the overhead line 1, is applied to the filter capacitor 6 via the current collector 2 and the filter reactor 4. The filter capacitor 6 smoothes the overhead line voltage applied from the overhead line 1. The filter reactor 4 and the filter capacitor 6 form a filter circuit. The inverter 7 has multiple switching elements 7a that form a three-phase bridge circuit. The inverter 7 is connected in parallel to the filter capacitor 6 and applies a variable voltage and variable frequency AC voltage to the propulsion motor 8 by pulse width modulation (PWM) control in asynchronous mode and synchronous mode.

[0013] Although FIG. 1 illustrates an overhead wire as the overhead line 1 and a pantograph-type current collector as the current collector 2, these configurations are not limited thereto. The overhead line 1 may be a third rail, as used in subways and the like, and the current collector 2 may be a third-rail current collector. Although FIG. 1 illustrates a case in which the overhead line 1 is a DC overhead line, the overhead line 1 may also be an AC overhead line. If the overhead line 1 is an AC overhead line, a transformer for stepping down the AC voltage to be received is provided between the current collector 2 and the switch 3a or between the switch 3a and the switch 3b, and a converter for converting the AC voltage output from the transformer to a DC voltage is provided downstream of the transformer. In the case of an AC overhead line, the increase in the overhead line voltage can be absorbed by the substation, but this places a burden on the substation. Therefore, the control method of the present invention, described below, is also useful for AC overhead lines in terms of reducing the burden on the substation.

[0014] A voltage detector 9 detects the voltage between the DC buses 14a and 14b as the overhead line voltage. A voltage detector 10 detects the filter capacitor voltage, which is the voltage of the filter capacitor 6. A current detector 11 detects the motor current flowing between the inverter 7 and the traction motor 8. A speed detector 16 detects the rotational speed of the traction motor 8.

[0015] The detected value of the overhead line voltage detected by the voltage detector 9, the detected value of the filter capacitor voltage detected by the voltage detector 10, and the detected value of the motor current detected by the current detector 11 are input to the control unit 12. In addition, the rotation speed detected by the speed detector 16 is input to the control unit 12 as speed information indicating the running speed of a train made up of one or more railcars coupled together.

[0016] It should be noted that well-known sensorless control may be applied to the propulsion control device 80. Sensorless control is a technique that estimates the motor speed or the rotor position of the propulsion motor 8 without using a speed sensor or position sensor, and controls the propulsion motor 8 based on the estimated motor speed information or position information. For this reason, when sensorless control is applied to the propulsion control device 80, the speed detector 16 is not necessary.

[0017] The brake chopper circuit 5 is connected in parallel to the filter capacitor 6 and the inverter 7. The brake chopper circuit 5 has a brake resistor 5a for consuming regenerative power generated in the traction motor 8, a switching element 5b connected in series to the brake resistor 5a, and a diode 5c connected in parallel to the brake resistor 5a. Note that the diode 5c can be omitted.

[0018] The control unit 12 controls the opening and closing of the switches 3a and 3b based on at least one of the detected values ​​of the overhead line voltage and the filter capacitor voltage. The control unit 12 also controls the operation of the traction motor 8 by outputting a PWM signal to the switching element 7a of the inverter 7 based on the detected values ​​of the overhead line voltage and the filter capacitor voltage. The control unit 12 also performs power consumption control, which causes the brake resistor 5a to consume the regenerative power generated by the traction motor 8, based on the filter capacitor voltage. Furthermore, the control unit 12 performs mode switching control, which switches between asynchronous and synchronous modes, based on the filter capacitor voltage and rotational speed information, which is information about the rotational speed of the traction motor 8, or vehicle speed information, which is information about the running speed of the railway vehicle on which the traction motor 8 is installed. The rotational speed information or vehicle speed information may be obtained by any means or method. If the traction motor 8 is equipped with a speed detector 16 as shown in FIG. 1, the detected value of the speed detector 16 can be used. Alternatively, if vehicle speed information managed by a train information management device (not shown) is available, the vehicle speed information can be used to convert the vehicle speed information into rotational speed information.

[0019] Fig. 2 is a diagram showing an example of the configuration of the PWM signal generating unit 50 provided in the control unit 12 shown in Fig. 1. As shown in Fig. 2, the PWM signal generating unit 50 is configured to include a voltage command calculation unit 55, an asynchronous carrier signal generating unit 57, a synchronous three-pulse carrier signal generating unit 58, a selection switch 59, a pulse mode switching processing unit 60, comparators 61 to 63, and inversion circuits 64 to 66.

[0020] The voltage command calculation unit 55 generates three-phase voltage commands, that is, a U-phase voltage command Vu*, a V-phase voltage command Vv*, and a W-phase voltage command Vw*, from the modulation factor PMF and the control phase angle θ based on the following equations (1) to (3).

[0021] Vu*=PMF·sinθ …(1) Vv*=PMF·sin(θ-(2π / 3)) …(2) Vw*=PMF·sin(θ-(4π / 3)) …(3)

[0022] The carrier signal CAR compared with each of the voltage commands is a signal selected by the pulse mode switching processor 60 using a selection switch 59 from asynchronous carrier signal A generated by asynchronous carrier signal generator 57, synchronous three-pulse carrier signal B generated by synchronous three-pulse carrier signal generator 58, and zero value C selected for one-pulse mode. The synchronous carrier signal is a signal whose frequency is determined as a function of inverter output frequency FINV so that the number and positions of pulses contained in the inverter output voltage are the same in the positive and negative half cycles of the inverter output voltage. The inverter output voltage is the voltage output by the inverter 7 to the traction motor 8, and the inverter output frequency FINV is the frequency of the inverter output voltage. The asynchronous carrier signal is a signal that is not a synchronous carrier signal, but a carrier signal with a frequency determined independently of the inverter output frequency FINV.

[0023] The U-phase voltage command Vu*, V-phase voltage command Vv*, and W-phase voltage command Vw* output from voltage command calculation unit 55 are compared in magnitude with carrier signal CAR in comparators 61 to 63, and the PWM signals U, V, and W are generated as the comparison results, and these are further passed through inversion circuits 64 to 66 to generate PWM signals X, Y, and Z. These PWM signals U, V, W, X, Y, and Z control inverter 7, which supplies the desired AC power to propulsion motor 8 and controls the operation of propulsion motor 8.

[0024] As described above, the PWM signal generator 50 has a synchronous pulse mode in which it generates and outputs a PWM signal in which the frequency of the inverter output voltage is synchronized with the frequency of the carrier signal used to generate the PWM signal, and an asynchronous pulse mode in which it generates and outputs a PWM signal in which the frequency of the inverter output voltage is not synchronized with the frequency of the carrier signal. The PWM signal generator 50 selects an appropriate pulse mode according to the vehicle speed and generates a PWM signal according to the selected pulse mode. The PWM signal generator 50 controls the operation of the traction motor 8 by outputting the generated PWM signal to the switching element 7a provided in the inverter 7.

[0025] Fig. 3 is a diagram illustrating the operation of the pulse mode switching process in the PWM signal generating unit 50 shown in Fig. 2. The horizontal axis of Fig. 3 represents the inverter output frequency FINV, and the vertical axis of Fig. 3 represents, from the top down, the modulation factor PMF, the transition of the pulse mode, and the transition of the selection operation of the selection switch 59.

[0026] When a railway vehicle accelerates from a stopped state, if the vehicle speed is low, i.e., if the inverter output frequency FINV is low, the modulation factor PMF is small, the pulse mode is the asynchronous multi-pulse mode, and the selector switch 59 selects A. In the asynchronous multi-pulse mode, the number of pulses included in a half cycle of the inverter output voltage is set to an integer value of 3 or greater.

[0027] On the other hand, when the vehicle speed increases and the modulation factor PMF becomes equal to or greater than PMF1, the output voltage of the inverter 7 becomes saturated in the asynchronous multi-pulse mode, so the selector switch 59 is switched to position B and the pulse mode is changed to the synchronous three-pulse mode. The synchronous three-pulse mode is a mode in which the number of pulses included in a half cycle of the inverter output voltage is always three. Note that the synchronous three-pulse mode is an example of a synchronous pulse mode, and the number of pulses included in a half cycle of the inverter output voltage can be set to an integer value of four or greater, not just three.

[0028] Furthermore, when the vehicle speed increases and the modulation factor PMF reaches PMF2, the selector switch 59 is switched to C to switch the pulse mode to the 1-pulse mode. The 1-pulse mode is a mode in which the number of pulses included in the half cycle of the inverter output voltage is always 1.

[0029] In addition, during regenerative braking when a railway vehicle uses regenerative braking to decelerate, in normal control where the possibility of regenerative braking failure is not detected, the pulse mode transitions from 1-pulse mode to synchronous 3-pulse mode to asynchronous multi-pulse mode in the reverse order to that described above, and selection switch 59 switches between C, B, and A in that order.

[0030] Next, the operation of the main parts in the first embodiment will be described. FIG. 4 is a diagram showing an operating curve provided for explaining the regenerative power control according to the first embodiment. In FIG. 4, the asynchronous multi-pulse mode and the synchronous three-pulse mode are collectively referred to as "multiple-pulse mode." FIG. 5 is a time chart provided for explaining the regenerative power control according to the first embodiment.

[0031] First, when the railway vehicle is decelerating, i.e., when regenerative braking is being performed, the control unit 12 constantly monitors the overhead line voltage and determines whether the overhead line voltage exceeds a threshold value in order to detect the possibility of regeneration failure. The threshold value is set to an arbitrary value less than the upper limit value based on the upper limit value of the overhead line voltage.

[0032] If the overhead line voltage exceeds the threshold, the control unit 12 reduces the command value of the motor applied voltage to the propulsion motor 8 to approximately 60 to 80% of the value during normal control. The command value of the motor applied voltage is synonymous with the modulation factor PMF. The operation at this time is shown in Figures 4 and 5. The control to reduce the command value of the motor applied voltage is carried out based on the overhead line voltage, regardless of the pulse mode.

[0033] In FIG. 4, the curve shown by the dashed-dot line is the operating curve of the motor applied voltage before the change, i.e., during normal control, and the curve shown by the broken line is the operating curve of the motor applied voltage after the change, i.e., during regenerative braking in embodiment 1. Also in FIG. 4, the curve shown by the dashed-dot line is the operating curve of the motor current before the change, i.e., during normal control, and the curve shown by the solid line is the operating curve of the motor current after the change, i.e., during regenerative braking in embodiment 1. The horizontal axis of FIG. 4 represents the inverter output frequency FINV. The inverter output frequency FINV is synonymous with the vehicle speed. During regenerative braking, the operating curve moves from right to left on the diagram. Note that the operating curve during normal control is the same as the operating curve during powering. Also, the horizontal axis of FIG. 5 represents time, and the operating curve moves from left to right on the diagram as time passes.

[0034] To obtain the required regenerative braking torque, the control unit 12 performs control to increase the motor current so as to compensate for the reduced motor applied voltage. This control causes the operating point of the motor current to move from the dashed dotted line shown in FIG. 4 to the solid line. This compensates for the reduction in regenerative power. In the example shown in FIG. 5, at time t1 when the overhead line voltage exceeds a threshold, the motor applied voltage is gradually reduced, and at time t2 when the increase in the overhead line voltage has subsided, the reduction in the motor applied voltage is stopped and the reduced motor applied voltage is maintained. Note that, as also shown in FIG. 5, control is performed to maintain the required regenerative braking torque regardless of whether or not the regenerative power control according to the first embodiment is performed.

[0035] Here, the loss generated in the stator winding of the traction motor 8 increases in proportion to the square of the motor current. Therefore, by implementing the regenerative power control according to the first embodiment, the regenerative power loss in the traction motor 8 can be increased compared to normal control, thereby reducing the possibility of regeneration failure. As a result, the dependency on the brake chopper circuit and brake shoes can be reduced, which prevents the brake chopper circuit from becoming larger and reduces brake shoe wear. This has the effect of preventing the brake chopper circuit from becoming larger and the maintenance intervals for the railway vehicle from becoming shorter.

[0036] Although the efficiency when the regenerative power control according to the first embodiment is performed is lower than that during normal control, the efficiency reduction occurs only during regenerative braking, and the impact of the reduction in efficiency is small. Furthermore, when comparing the disadvantage of the reduction in efficiency only during regenerative braking with the advantage of being able to suppress an increase in the size of the brake chopper circuit and shorten the maintenance intervals for the railway vehicle, it is no exaggeration to say that the latter advantage is greater.

[0037] An example of a flow for carrying out the above-described control is shown in Fig. 6. Fig. 6 is a flowchart illustrating regenerative power control according to the first embodiment.

[0038] The control unit 12 monitors the overhead line voltage (step S11) and determines whether the overhead line voltage has exceeded a first threshold value (step S12). If the overhead line voltage has exceeded the first threshold value (step S12, Yes), the control unit 12 performs regenerative power control to reduce the motor applied voltage below the command voltage (step S13). The "command voltage" here refers to the command value of the motor applied voltage during normal control. After step S13, the processing continues from step S11. In this paper, the regenerative power control performed in step S13 will be referred to as the "first control" where appropriate.

[0039] Furthermore, if the overhead line voltage does not exceed the first threshold (step S12, No), the control unit 12 determines whether the overhead line voltage has dropped to or below the second threshold (step S14). In the flow of FIG. 6, the second threshold is set to a value smaller than the first threshold and is introduced to prevent control fluctuations. If the overhead line voltage has not reached the second threshold (step S14, No), the control unit 12 continues the current control (step S15). That is, if the regenerative power control according to the first embodiment is being performed, the control unit 12 continues the regenerative power control, and if normal control is being performed, the control unit 12 continues the normal control. After step S15, the processing continues from step S11.

[0040] Furthermore, if the overhead line voltage drops below the second threshold (step S14, Yes), the control unit 12 performs control to return the motor applied voltage to the command voltage (step S16). The control to return the motor applied voltage to the command voltage means temporarily stopping the regenerative power control according to the first embodiment and returning to normal control. After step S16, the processing continues from step S11.

[0041] The determination process in step S12 using the first threshold value and the determination process in step S14 using the second threshold value make it possible to prevent the control by the control unit 12 from fluctuating between regenerative power control and normal control. Note that in the determination process in step S12 above, the case where the overhead line voltage is equal to the first threshold value is determined as "No," but it may also be determined as "Yes." In other words, the case where the overhead line voltage is equal to the first threshold value may be determined as either "Yes" or "No." Also, in the determination process in step S14 above, the case where the overhead line voltage is equal to the second threshold value is determined as "Yes," but it may also be determined as "No." In other words, the case where the overhead line voltage is equal to the second threshold value may be determined as either "Yes" or "No."

[0042] Note that, although Fig. 5 shows an example in which the rise in the overhead line voltage subsides at time t2, if the rise in the overhead line voltage does not subside even after the motor applied voltage reaches the allowable lower limit, control that increases the loss in the inverter 7 may also be used. In this paper, the following first and second methods are illustrated.

[0043] The first method is to increase the number of switching operations in PWM control. Increasing the number of switching operations can increase the switching loss in the inverter 7. This allows a portion of the regenerative power generated by the propulsion motor 8 to be converted into switching loss and consumed by the inverter 7, thereby complementing the regenerative power control described above.

[0044] The second technique involves switching the pulse mode to a pulse mode with more pulses than the current one, i.e., switching the current pulse mode to a pulse mode with an increased number of pulses included in the PWM signal. For example, if the current pulse mode is a one-pulse mode, control is performed to switch to a synchronous three-pulse mode or an asynchronous multi-pulse mode. Also, if the current pulse mode is a synchronous three-pulse mode, control is performed to switch to an asynchronous multi-pulse mode with a number of pulses greater than three. Also, if the current pulse mode is a five-pulse asynchronous multi-pulse mode, control is performed to switch to an asynchronous multi-pulse mode with a number of pulses greater than five. This can increase switching loss in the inverter 7 and harmonic loss in the traction motor 8. This allows a portion of the regenerative power to be consumed by the inverter 7 and the traction motor 8, complementing the regenerative power control described above.

[0045] Next, a hardware configuration for realizing the functions of the control unit 12 described above will be described with reference to the drawings of Fig. 7 and Fig. 8. Fig. 7 is a block diagram showing an example of a hardware configuration for realizing the functions of the control unit 12 according to embodiment 1. Fig. 8 is a block diagram showing another example of a hardware configuration for realizing the functions of the control unit 12 according to embodiment 1.

[0046] When realizing some or all of the functions of the control unit 12 according to embodiment 1, the configuration can include a processor 300 that performs calculations, a memory 302 that stores programs read by the processor 300, and an interface 304 that inputs and outputs signals, as shown in FIG. 7.

[0047] The processor 300 is a computing means. The processor 300 may be a computing means called a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). Examples of the memory 302 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (Electrically EPROM), as well as magnetic disks, flexible disks, optical disks, compact disks, minidisks, and DVDs (Digital Versatile Discs). The memory 302 may be a combination of multiple storage devices, such as a combination of RAM and EEPROM.

[0048] The memory 302 stores a program that executes the functions of the control unit 12 according to the first embodiment. The processor 300 exchanges necessary information via the interface 304, executes the program stored in the memory 302, and refers to the table stored in the memory 302, thereby performing the above-described processing. The calculation results by the processor 300 can be stored in the memory 302.

[0049] 8 can be used to implement part of the functions of the control unit 12 according to the first embodiment. The processing circuit 303 may be a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. Information to be input to the processing circuit 303 and information to be output from the processing circuit 303 can be obtained via an interface 304.

[0050] It is also possible that some of the processing in the control unit 12 is performed by the processing circuit 303, and the processing that is not performed by the processing circuit 303 is performed by the processor 300 and the memory 302.

[0051] As described above, the propulsion control device according to the first embodiment includes a filter capacitor, an inverter connected in parallel to the filter capacitor, and a control unit that controls the inverter based on the overhead line voltage and the filter capacitor voltage. The filter capacitor smoothes the overhead line voltage applied from the overhead line. The inverter applies a variable voltage and variable frequency AC voltage to the traction motor mounted on the railway vehicle. When the overhead line voltage exceeds a first threshold during regenerative operation of the traction motor, the control unit performs a first control that reduces the motor application voltage applied to the traction motor below a command voltage. By performing the first control, the control unit increases the motor current so as to maintain a required regenerative brake torque. The increase in motor current increases the loss of regenerative power compared to before the first control was performed. This reduces the possibility of regeneration failure, thereby achieving the effects of suppressing the increase in the size of the brake chopper circuit and the shortening of the maintenance interval of the railway vehicle.

[0052] When the above-described first control is performed, the control unit may perform control to return the motor applied voltage to the command voltage if the overhead line voltage drops to or below a second threshold value that is smaller than the first threshold value. This provides the advantage of preventing the control by the control unit from fluctuating between the first control and normal control that does not perform the first control.

[0053] Furthermore, when the first control is performed, the control unit may increase the number of switching operations in the PWM control to increase the switching loss. In this way, a portion of the regenerative power generated by the propulsion motor can be converted into switching loss and consumed by the inverter. This complements the first control and enhances the effects of the first embodiment.

[0054] Furthermore, when the first control is performed, the control unit may switch the current pulse mode to a pulse mode in which the number of pulses included in the PWM signal is increased. This increases the switching loss in the inverter and the harmonic loss in the propulsion motor. This complements the first control and enhances the effects of the first embodiment.

[0055] Embodiment 2 Fig. 9 is a diagram showing an operating curve used to explain regenerative power control according to the second embodiment. Although not described in the first embodiment, the operating curve shown in Fig. 4 shows that the command value for the reduced motor applied voltage is maintained at a constant value regardless of the vehicle speed, and that normal control is restored when the command value for the reduced motor applied voltage matches the operating curve before the change. In contrast, the operating curve shown in Fig. 9 shows that the command value for the motor applied voltage is maintained at a constant value, and that the command value for the motor applied voltage decreases linearly in the low-speed range where the vehicle speed is low.

[0056] In the second embodiment, it is intended to continue control to increase the loss of regenerative power even in low-speed regions where the vehicle speed is low. As shown in FIG. 9, when the vehicle speed drops below a predetermined first speed v1, the control unit 12 performs control to linearly decrease the command value of the motor applied voltage. This control is referred to as "second control" as appropriate in this document. This second control makes it possible to increase the loss of regenerative power even in low-speed regions where the vehicle speed is low. This reduces the possibility of regeneration failure compared to the first embodiment. Note that the vehicle speed information may be obtained using the value detected by the speed detector 16, or may be obtained using vehicle speed information managed by a train information management device (not shown).

[0057] As described above, the propulsion control device according to the second embodiment performs the second control, which linearly reduces the motor applied voltage, when the railway vehicle speed drops below the first speed during the first control. This second control increases the loss of regenerative power even in the low-speed range where the vehicle speed is low. This has the effect of reducing the possibility of regeneration failure compared to the first embodiment.

[0058] When implementing the second control, the control unit may also implement the switching control described in the first embodiment, i.e., control that increases the number of switching times in PWM control to increase switching loss. This complements the first and second controls, thereby enhancing the effect of the second embodiment. The control unit may also implement the pulse mode switching control described in the first embodiment, i.e., control that switches the current pulse mode to a pulse mode in which the number of pulses included in the PWM signal is increased. This complements the first and second controls, thereby enhancing the effect of the second embodiment.

[0059] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0060] For example, if the railway vehicle traction system 100 is equipped with a storage battery, the first and second controls described above may be implemented when the storage battery is fully charged. Also, if the railway vehicle traction system 100 is equipped with a generator, the regenerative power generated by the traction motor 8 may be supplied to the generator, and the regenerative power may be consumed by passing a current through the stator windings of the generator. In addition, various aspects of the present disclosure are summarized below as appendices. [Appendix 1] a filter capacitor that smoothes the overhead line voltage applied from the overhead line; an inverter connected in parallel to the filter capacitor and applying a variable voltage and variable frequency AC voltage to a traction motor mounted on the railway vehicle; a control unit that controls the inverter based on the overhead line voltage and a filter capacitor voltage that is the voltage of the filter capacitor; Equipped with When the overhead line voltage exceeds a first threshold during a regenerative operation of the traction motor, the control unit performs a first control to reduce a motor applied voltage applied to the traction motor to a value lower than a command voltage. A propulsion control device characterized by: [Appendix 2] When the overhead line voltage drops to or below a second threshold value that is smaller than the first threshold value during the first control, the control unit performs control to return the motor applied voltage to the command voltage. 2. The propulsion control device according to claim 1, [Appendix 3] the control unit includes a pulse width modulation signal generating unit that outputs a pulse width modulation signal to a switching element provided in an inverter to control an operation of the propulsion motor; The control unit increases the number of switching times in pulse width modulation control when the first control is performed. 3. The propulsion control device according to claim 1 or 2. [Appendix 4] the control unit includes a pulse width modulation signal generating unit that outputs a pulse width modulation signal to a switching element provided in an inverter to control an operation of the propulsion motor; the pulse width modulation signal generation unit has a synchronous pulse mode in which it generates and outputs a pulse width modulation signal in which the frequency of the output voltage of the inverter is synchronized with the frequency of a carrier signal used to generate the pulse width modulation signal, and an asynchronous pulse mode in which it generates and outputs a pulse width modulation signal in which the frequency of the output voltage of the inverter is not synchronized with the frequency of the carrier signal, The control unit switches the current pulse mode to a pulse mode in which the number of pulses included in the pulse width modulation signal is increased when the first control is performed. 3. The propulsion control device according to claim 1 or 2. [Appendix 5] When the speed of the railway vehicle decreases to a first speed or less during the first control, the control unit performs a second control to linearly decrease the motor applied voltage. 5. The propulsion control device according to any one of claims 1 to 4. [Appendix 6] the control unit includes a pulse width modulation signal generating unit that outputs a pulse width modulation signal to a switching element provided in an inverter to control an operation of the propulsion motor; The control unit increases the number of switching times in pulse width modulation control when the second control is performed. 6. The propulsion control device according to claim 5, [Appendix 7] the control unit includes a pulse width modulation signal generating unit that outputs a pulse width modulation signal to a switching element provided in an inverter to control an operation of the propulsion motor; the pulse width modulation signal generation unit has a synchronous pulse mode in which it generates and outputs a pulse width modulation signal in which the frequency of the output voltage of the inverter is synchronized with the frequency of a carrier signal used to generate the pulse width modulation signal, and an asynchronous pulse mode in which it generates and outputs a pulse width modulation signal in which the frequency of the output voltage of the inverter is not synchronized with the frequency of the carrier signal, The control unit switches the current pulse mode to a pulse mode in which the number of pulses included in the pulse width modulation signal is increased when the second control is performed. 6. The propulsion control device according to claim 5, [Explanation of symbols]

[0061] 1 overhead line, 2 current collector, 3a, 3b switches, 4 filter reactor, 5 brake chopper circuit, 5a brake resistor, 5b, 7a switching element, 5c diode, 6 filter capacitor, 7 inverter, 8 propulsion motor, 9, 10 voltage detector, 11 current detector, 12 control unit, 14a, 14b DC bus, 16 speed detector, 50 PWM signal generator, 55 voltage command calculation unit, 57 asynchronous carrier signal generator, 58 synchronous 3-pulse carrier signal generator, 59 selection switch, 60 pulse mode switching processing unit, 61 to 63 comparators, 64 to 66 inversion circuits, 80 propulsion control device, 100 railway vehicle drive system, 300 processor, 302 memory, 303 processing circuit, 304 interface.

Claims

1. a filter capacitor that smoothes the overhead line voltage applied from the overhead line; an inverter connected in parallel to the filter capacitor and applying a variable voltage and variable frequency AC voltage to a traction motor mounted on the railway vehicle; a control unit that controls the inverter based on the overhead line voltage and a filter capacitor voltage that is the voltage of the filter capacitor; Equipped with the control unit performs a first control to reduce a motor applied voltage applied to the propulsion motor to a value lower than a command voltage when the overhead line voltage exceeds a first threshold during a regenerative operation of the propulsion motor; If the increase in the overhead line voltage does not converge even after the motor applied voltage reaches an allowable lower limit, a second control is performed to linearly decrease the motor applied voltage when the speed of the railway vehicle decreases to a first speed or less. A propulsion control device characterized by:

2. the control unit includes a pulse width modulation signal generating unit that outputs a pulse width modulation signal to a switching element provided in the inverter to control an operation of the propulsion motor; The pulse width modulation signal generating unit is configured to: a synchronous pulse mode in which a pulse width modulation signal is generated and output in which the frequency of the output voltage of the inverter is synchronized with the frequency of a carrier signal used to generate the pulse width modulation signal; an asynchronous pulse mode in which a pulse width modulation signal in which the frequency of the output voltage of the inverter and the frequency of the carrier signal are not synchronized is generated and output; a one-pulse mode in which the number of pulses included in a half cycle of the inverter output voltage is always one; When the increase in the overhead line voltage does not converge even after the motor applied voltage reaches an allowable lower limit value, the control unit switches the current pulse mode to a pulse mode in which the number of pulses included in the pulse width modulation signal is increased when the first and second controls are performed.

2. The propulsion control device according to claim 1 .

3. When the pulse mode is the one-pulse mode, the control unit switches the pulse mode to the synchronous pulse mode or the asynchronous pulse mode according to the amount of decrease in the voltage applied to the motor.

3. The propulsion control device according to claim 2.

4. When the overhead line voltage drops to or below a second threshold value that is smaller than the first threshold value during the first control, the control unit performs control to return the motor applied voltage to the command voltage.

4. The propulsion control device according to claim 1, wherein the propulsion control device is a propulsion control device.

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